Fiber glass reinforced thermoplastic resinous sheet have been described in U.S. Pat. No. 3,664,909. Sheet materials described in the aforementioned patent have found utility in that they can be stamped in a mechanical press to produce shaped articles for various uses such as automotive seat shells, battery trays, luggage, musical instrument cases and the like.
The process typically employed to produce shaped articles from fiber glass reinforced thermoplastic sheets are described in U.S. Pat. Nos. 3,621,092 and 3,626,053.
Fiber glass reinforced thermoplastic sheets have also found utility in sheet form as liners for fleet trucks and as base board materials for ice hockey arenas and other applications requiring high impact strength.
In general the process for preparing thermoplastic resin sheets for either stamping or for use in sheet form has been the same with respect to the fiber glass mat employed to reinforce the resin. Thus, in preparing sheets for use as a stampable material or as a sheet material not requiring further stamping the mat has been prepared by laying down the continuous glass fiber strands on a moving conveyor chain. The process conventionally employed to produce such a continuous strand is described in U.S. Pat. No. 3,883,333. As described in this patent, which is hereby incorporated by reference, the mat after formation on the conveyor chain is subsequently needled just prior to be collected. In the past this needling has been conducted to provide a plurality of penetrations of the mat by the needles and good entanglement of the strands to mechanically bond the mat. At the same time, the action of the needles in catching the strands in barbs and pushing them through the bed plate and having them returned as the mat moves horizontally places a plurality of broken filaments in the mat rendering it useful for reinforcing resinous sheets that are to be stamped. The broken filaments move with the resin during the stamping operation to insure that the resin flowing to the ends of the mold is properly reinforced with glass.
While this process has proved efficacious in producing high strength materials from glass reinforced thermoplastic sheets that are stamped to produce, for example, automotive parts considerable improvement is desired in the flexural strength characteristics of the sheet products manufactured from such mats when the product is to be utilized in sheet form.